Flat Vacuum Solar Collector Having Chamber-Type Heads

ABSTRACT

The invention relates to a flat solar collector comprising individual vacuum chambers. The invention is formed by two heads and a series of parallel tubes having high transmittance in the solar spectrum, which is disposed between said heads. The opposite side of the heads is provided with vacuum chambers which closure the connections of the conducting tubes. One of the vacuum chambers is characterized in that it is fitted with a vacuum valve at one end thereof. In addition, conducting tubes are disposed inside the aforementioned tubes having high transmittance in the solar spectrum and said conducting tubes are in turn connected to collector plates, all under vacuum conditions which minimize convection energy losses. When the conducting tubes are configured in series, the collector can raise the temperature of the working fluid to above 200° C. All of the above is performed in a novel, simple and economical manner.

FIELD OF INVENTION

This invention refers to a device which provides an improvement in solarenergy collection and conservation, in thermal solar collectors. Thedevice is formed by using conventional components, which allowsguaranteeing a better efficiency and a reduction in manufacturing cost.

BACKGROUND

This invention is directly related with flat solar collectors, which areused to absorb solar energy and transferring it to a fluid. Moreover, itis linked with flat vacuum solar collectors which provide vacuum betweena collection plate and a glass closure to obtain a better performance.

Since time ago it is known that flat vacuum solar collectors are themost reliable of its kind, due to simplicity in their structure and lowoperating temperatures. These low operating temperatures do not damagethe commercial materials being used in their manufacturing. However,collectors which are able to transfer a higher amount of energy to afluid have been demanded in recent times, and a number of promisingtechnologies have been achieved.

A reason why flat solar collectors do not reach high temperatures ismainly due to the convection effect. In these collectors, the mainenergy loss is due to the produced convection since the collecting plateis at a different temperature than the glass plate (collector closure).A number of different methods have been proved with the passage of timeto prevent this effect, such as plate panels (hexagonal shape surfaces),by assembling a double glass plate, and creating a vacuum between thecollector plate and the glass plate. This last method is the mostcommonly used, but requires a more rough structure than the conventionalflat collector to support the vacuum caused stresses. In order toprovide the required structural support to withstand these efforts, thecollector structure has been modified, but a device is not yet availableto reach the desired temperature without requiring costly, specializedmaterials and a troublesome manufacturing process.

In order to get an outlet temperature in the collector higher than 200°C. using commercial parts and simple manufacturing processes, thepresent device has been developed. Said device comprises hightransmittance in solar spectrum tubes (TATES) closed in the end sides bya pair of heads attached to small vacuum chambers. The only TATES whichare not closed by the vacuum chambers, are those with working fluidinlet and outlet. Within these TATES conducting tubes (TUCS) made of anythermal conducting material are located, attached to collector platesand closed with a selective surface in the solar spectrum to absorb thelargest possible amount of energy. These TUCS are arranged over lowthermal conduction supports, preferably ceramics, in order to lose theleast possible amount of energy by conduction. By means of a vacuum pumpcoupling, a vacuum is created within the high transmittance in solarspectrum tubes and the vacuum chambers, which allows reachingtemperatures higher than 200° C. The present invention is different frompreviously designed devices due to several factors, most relevant ofthem disclosed below. The first difference is that flat vacuum solarcollectors in the past (U.S. Pat. No. 4,038,965-Lyon, U.S. Pat. No.4,281,642-Steinberg, U.S. Pat. No. 4,289,113-Whittemore, U.S. Pat. No.5,653,222-Newman) were designed in such a way that they all have a base,and a glass plate which closes the collector at all. These have a severetechnical problem, since stresses created by a pressure differencewithin the collector and the atmospheric pressure, distort the structureand make it to fail, which causes a loss in vacuum within the collector.Lyon and Whittemore use linear supports which are attached along thecollector so that they prevent distortion of the collector containingbox. Steinberg designed a complex support which is located within thebox. This support is a series of semicircles, which provide support tothe glass closure on one side, while providing box support on the otherside. Finally, Newman proponed a less complex solution, which uses aglass closure for the top of collector but the bottom thereof iscomprised of semicircles, the semicircle peaks serve as a support forthe top portion. In present invention the problem of pressure differenceis solved by using high transmittance in solar spectrum tubes, whichprovide a smoothly spread stress distribution between said tubes.Another important problem having the above mentioned collectors is thatglass thermal expansion and that from the base is different, whichcauses vacuum losses. The expansion of one piece depends on both thethermal expansion coefficient and the piece size. This is not a problemunder present invention, since the only expansion which producessignificant differences is the one occurring along the hightransmittance in solar spectrum tubes and the conducting tubes, butbecause of the collector assembly form, said expansion does not causeany vacuum losses since having enough space for conducting tubedifferential expansion. Newman proposes in his design that temperedglass is used on top closure and then a series of treatment is providedto improve the glass optical properties, while under present inventioncommercial tubes showing better optical and thermal properties are usedwithout any need to subject them to any additional treatment.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a general view of a flat vacuum solar collector.

FIG. 2 is a top view of a collector.

FIG. 3 is a cross-sectional view A-A of FIG. 2.

FIG. 4 a is rear view of one of the heads.

FIG. 4 b is a top view of one of the heads.

FIG. 4 c is a front view of one of the heads.

DETAILED DESCRIPTION OF INVENTION

The present invention represented in FIGS. 1 and 3 is a flat solarcollector comprising an arrangement of High Transmittance in SolarSpectrum Tubes, herein and forth “TATES” (2), aligned in parallel andclosed in their end sides by a pair of heads (1) and attached to smallvacuum chambers (3).

Within each TATES and longitudinally arranged is a conducting tube(TUCS) (9) with a lower diameter than TATE, which transport the workingfluid, TUCS are composed of any thermal conducting material, and eachTUCS has attached along its length, a collecting plate (8) covered witha selective surface in solar spectrum to absorb the most possible amountof solar energy. These TUCS are arranged on low thermal conductionsupports, preferably ceramics (10) to minimize the energy losses byconduction.

Each TATES end is closed by a head (1); the heads are preferablyrectangular, having small punctures aligned along the head, thispunctures have a larger diameter than TUCS to allow passing themtherein. The number of circular punctures coincides with the number ofTUCS, and the head side which is attached to TATES is named front sideand the opposite one, rear side; being through this side where thesevacuum chambers are joined (3), being of an area such that covers thecross-sectional area of 2 TATES. Vacuum chambers cover and are groupingin pairs the head circular punctures, where TUCS (9) are introduced.TUCS are located in parallel and they are joined each other, within thevacuum chamber by 90° or 180° elbows. The only circular punctures whichare not covered by vacuum chambers are the first circular puncture orinlet puncture (6) and the last circular puncture or outlet puncture (7)from conducting tubes (TUCS) (9) which carry the working fluid. Theseare the only two contact points, no matter what the amount of TUCScomprising the solar collector is, with the feature that in this andlast circular puncture the thermal expansion coefficient is differentfrom the remaining.

For vacuum control and generation, at least on vacuum generation pump(4), and a pressure level meter (5) are connected to one of the vacuumchambers (3), which allows to generate the vacuum within the TATES andvacuum chambers, that is, in case that the vacuum within the system islost, it is possible to recover it without requiring a systemreplacement and allowing additionally to control vacuum levels to keep adetermined temperature thus preventing a modification in fluidtemperature and flow. Because of that, the vacuum level in turn allowsthat TUCS reach temperatures higher than 200° C.

It may be noted from FIGS. 1, 2, 4 a, 4 b and 4 c that the collector isa sealed device and composed by a variety of conventional elements whichwhen being integrated achieve a non-conventional thermal performance.For improving the TATES performance (2), these are preferably built fromborosilicate glass since due to its high compression mechanical strengththey may reach a high vacuum level, which was impossible in other flatvacuum solar collectors.

Heads (1) are more detailed shown in FIGS. 4 a, 4 b and 4 c. In FIG. 4 cit is noted that the head is preferably rectangular and a number ofbores are aligned in its front side equivalent to the amount of TATES(2) forming the solar collector. Surrounding these bores, circular slots(11) with the same diameter than TATES (2) are located and having adepth about the same than the TATES wall width (provided that this depthdoes not weaken excessively the head wall (1). Upon assembling theTATES(2) in heads (1) these circular slots (11) are filled with amaterial which prevents vacuum leakages, where said material may begrease, silicone or structural glue, the last being preferable. Assemblyshould be carried out once glue is dried to guarantee a vacuum leakagefree joint between TATES and heads.

In FIG. 4 a, the head rear side is seen where other slots are noticed(12) for vacuum chambers (3), which gather the bores whereby TUCS arepassed, in such a way that when the TUCS number is odd, one of the boresat edge does not carry a slot, while when the number of TATES connectedto heads is pair, the end side bores are always surrounded by a slot(12). Slots (12) shall be of a similar area to vacuum chambers (3), andwith a depth about the same than the chamber wall width provided it doesnot excessively weaken the head wall (1). In the assembly process, theseslots (12) are preferably filled with a structural glue, and vacuumchambers are inserted (3) inside the heads (1) before the glue is dried,in such a way that a vacuum leakage free joint is achieved between thevacuum chambers (3) and the heads (1).

One of the most important elements of this invention are the hightransmittance in solar spectrum tubes (TATES), which shall be preferablyof borosilicate glass, since these tubes show high optical, thermal andmechanical properties beneficial for collector performance. For examplea common borosilicate glass tube will transmit more than 92% of theenergy received from the sun and would reflect a negligible percentage(a common glass cannot reach these properties unless subjected toseveral additional treatments after manufacturing). Another importantproperty is that its thermal expansion coefficient is so low that allowsa wide material selection for head manufacturing (1). These TATES (2)shall be preferably of an outer diameter higher than 50 mm to adjustinternally the conducting tubes (TUCS) with its respective collectingplate, as well as the support means. TATES are an ideal element sincetheir circular cross-sectional surface show a smooth stress distributionin vacuum and therefore a need to add additional supports isnonexistent. Another element is the vacuum chambers (3); which serve ashead closures (1), these are preferably built of glass tubes with adepth larger than 5 mm, although the cross section of these chambers maybe circular, elliptic and polygonal, provided that fulfills the functionof covering with one of their cross-sectional ends two adjacent TUCS.The use of glass is recommended since in this way takes advantage of thejoint and elbow collecting surface which connect among them the TUCS.These vacuum chambers (3) may be of regular or borosilicate glass. It isworth to mention that some of these chambers carry a coupling to connecta vacuum pump (4) in the opposite end to the one on contact with thehead, which allows to generate an initial vacuum or to recover thevacuum in case that due to any event a loss may exist. It is advisablethat in another one of the vacuum chambers (3), preferably in theopposite side of a vacuum chamber (3) with vacuum pump (4), a pressureindicator (5) is installed, with which the existing vacuum level may bemeasured and the type of leakage if any. Another important feature whichmay be noticed in FIG. 1 is the working fluid inlet which for operationin these collectors is generally water. This inlet as not being in avacuum chamber includes a package which contains the vacuum within thecollector.

In FIG. 2 the same previously disclosed features may be observed. Theamount of TATES (2) shall be determined by the working fluid flow andtemperature to be observed, but sometimes at least two serial orparallel vacuum chamber solar collectors will be required to achievethese goals, thus obtaining a flat solar collector system. Having thisin mind, it should be considered that for an odd TATES number (2), theTUCS inlet (6) and outlet (7) carrying the working fluid are each ineach head (1), while when the TATES (2) number is even, TUCS inlet (6)and outlet (7) carrying the working fluid are located in the same head(1).

In FIG. 3, a detail is shown of a cross-sectional view in point A-Arepresented by FIG. 2; the different elements comprising each TATESinner part in the solar collector may be observed. Beginning with theupper part, a collector plate (8) is firstly located, which is whetherwelded or attached to the conducting tube (TUCS) (9) carrying theworking fluid and the TUCS (9) stand on low thermal transmissionsupports, preferably ceramics (10). Within the vacuum chambers (3) thejoints among the TUCS (9) are located, depending on the arrangement tobe used (serial or parallel).

Collector plates (8) are made of a thermal conducting material(preferably copper). These collector plates (8) shall be of a thicknessnot larger than 0.2 mm and their length shall be shorter than each TATES(2) on each end depending on the circular slot (11) depth. Their widthshall be also a minimum of 95% from TATES (2) diameter, and the maximumdimension of these plates shall be only determined by the collectorplate material thermal expansion (8), since in any time these will nottouch the TATES (2) because that would cause heat losses by contact.Another important feature of collector plates (8) is that these arecoated by a solar spectrum selective surface on both sides. Togetherwith these collector plates (8) the TUCS (9) are located which carry theworking fluid. The joint between these components is carried out byusing any additive which allows a maximum possible heat transmission,such as silver welding. The TUCS (9) are also coated with a selectivesurface, preferably black chromium. This selective surface shall have ahigh solar spectrum monochromatic absorptivity and a low solar spectrummonochromatic emittance to be a candidate for use in a collector. Allthe thermal conducting material angles of this selective surface arecoated since in special cases concentrators may be arranged together tothe collector and directing their light beam to the concentrator bottom,since being the TATES (2) bottom would pass the same energy passing inthe top portion (more than 92%). TUCS and collector plate assemblystands on support means (10) made of a thermal insulating material (e.g.ceramics) so that the largest possible amount of energy is transferredto the working fluid. These supports (10) may be substituted by designshaving a lower contact surface with the TUCS (9) or with the TATES (2).In the vacuum chamber ends (3) is where the TUCS attachment is made.Materials within the vacuum chambers (3) generally form 180° elbowswhich are also coated with a solar spectrum selective surface, in orderto take advantage as much as possible from solar energy.

A flat vacuum solar collector with chamber type heads is possible tooperate by fulfilling with all previous disclosure, which may raise theworking fluid temperature higher than 200° C. since vacuum prevents thatconvection is present, then conduction losses are only present. Theselosses are very small since the contact is with insulating materials. Inaddition, a 100% of the piping for solar energy absorption may be usedsince everything is enclosed within containers with high solar spectrumtransmittance.

1. A flat solar collector with vacuum chambers characterized bycomprising at least two high transmittance in solar spectrum tubes,arranged in parallel, with the same diameter and length; limited on eachend side by a plate comprising in its whole length a number of alignedcircular punctures, with a lower diameter than the high solar spectrumtransmittance pipe diameter; the plate in one of its sides, havingcircular slots which diameter matches with the high transmittance tubediameter; and in the opposite side they have larger slots surrounding inpairs the circular punctures; a support of low thermal conduction islocated inside each high transmittance tube with a conducting tube oflower diameter than the plate circular punctures being arrangedlongitudinally thereon; passing through them and protruding by the platerear side; the protruding conducting tube end sides are located in theplate rear side and connected each other by means of elbows; at least avacuum chamber over which means to generate and recover vacuum and meansfor measuring a pressure level are possible to be arranged, is locatedin the same plate rear side matching with the larger slot.
 2. A flatsolar collector with vacuum chambers according to claim 1, characterizedin that heads are preferably rectangular, having 2 or more circularpunctures aligned along the head; a “circular slot” surrounding eachcircular puncture is located in the head front side, the number of“circular slots” is equivalent to the amount of high transmittance insolar spectrum tubes used for the solar collector.
 3. A flat solarcollector with vacuum chambers according to claim 2, characterized inthat the “circular slots” have the same diameter than the hightransmittance in solar spectrum tubes and having a depth about the samethan the high transmittance tube wall width.
 4. A flat solar collectorwith vacuum chambers according to claim 3, characterized in that thehigh transmittance in solar spectrum tubes are optionally joined withgrease, silicone and structural glue.
 5. A flat solar collector withvacuum chambers according to claim 1, characterized in that the rearside heads have slots in larger amounts equivalent to the hightransmittance in solar spectrum tubes less 1; said slots are insertedand joined with grease, silicone or preferably structural glue, thevacuum chambers grouping in pairs the end sides protruding from theconducting tubes and leaving without grouping the conducting tubeswherein the working fluid is entering and leaving; said vacuum chambersare arranged in a position where a set of 2 consecutive conducting tubesmay be covered.
 6. A flat solar collector with vacuum chambers accordingto claim 4, characterized in that the number of high transmittance tubesis odd in the rear side of both heads, one of the edge bores does notinclude a slot, while when the number of high transmittance tubes iseven, the edge bores in one of the heads is always framed by a slotwhile in the other head, the edge bores are not framed by a slot. Slotsshall be of a similar dimension to the vacuum chambers, and with a depthapproximately the same than the chamber wall width.
 7. A flat solarcollector with vacuum chambers according to claim 4, characterized inthat each conducting tube is covering a collector plate length and theconducting tubes stand on low or null thermal transmission supports,preferably ceramics, and said supports in turn stand on the hightransmittance in solar spectrum tubes.
 8. A flat solar collector devicewith vacuum chambers according to claim 6, characterized in that thecollector plates are located in parallel to the head top portion andbeing covered by a selective surface in both sides, in addition theattachment means between collector plates and conducting tubes may be ofa welded, pressed, glued base or any other attachment means whichefficiently transmits energy therein.
 9. A flat solar collector withvacuum chambers according to claim 1, characterized in that the hightransmittance tubes have preferably an outer diameter of 50 mm.
 10. Aflat solar collector with vacuum chambers according to claim 1,characterized in that the vacuum chambers are preferably built withglass tubes and having a bottom larger than 5 mm, with a circular,elliptic, or polygonal cross-section, preferably elliptic.
 11. A flatsolar collector with vacuum chambers according to claim 1, characterizedin that when the number of high transmittance tubes is odd, theconducting tube inlet and outlet transporting the working fluid arelocated one on each head, while when the number of high transmittancetubes is even, the conducting tube inlet and outlet transporting theworking fluid are located in the same head.
 12. A flat solar collectorwith vacuum chambers according to claim 1, characterized in that thehigh transmittance in solar spectrum tubes form a geometric structureproviding a body to the solar collector device.
 13. A flat solarcollector device with vacuum chambers according to claim 1,characterized in that the conducting tubes y and the collector platesare coated with a high monochromatic absorptivity selective surface anda low monochromatic emittance in solar spectrum or they are painted withhigh temperature resistant reflection preventing black paint, whichallows taking advantage of the solar energy.
 14. A flat solar collectorwith vacuum chambers according to claim 1, characterized in that theconducting tubes are attached among them by means of elbows, and theelbows are coated with a high monochromatic absorptivity selectivesurface or they are painted with high temperature resistant reflectionpreventing black paint, which allows taking advantage of the solarenergy.
 15. A flat solar collector with vacuum chambers according toclaim 1, characterized in that within each high transmittance in solarspectrum tube is located a conducting tube.
 16. A flat solar collectorwith vacuum chambers according to claim 1, characterized in that thehigh transmittance in solar spectrum tubes are preferably ofborosilicate glass but they may be of any material which efficientlytransmits solar energy.
 17. A flat solar collector with vacuum chambersaccording to claim 1, characterized in that there is sufficient spacewithin the vacuum chamber for conducting tube thermal expansion.
 18. Aflat solar collector with vacuum chambers according to claim 1,characterized in that the joint within the vacuum chamber between theconducting tubes is carried out by means of 90° or 180° elbows.
 19. Aflat solar collector with vacuum chambers according to claim 1,characterized in that vacuum is generated by means of a vacuumgenerating pump and being able to recover and control as required.
 20. Aflat solar collector with vacuum chambers according to claims 1,characterized in that the collector device may increase the workingfluid temperature up to more than 200° C.
 21. A flat solar collectorsystem with vacuum chambers, characterized in that at least two flatsolar collectors with vacuum chambers are serially or parallel connectedaccording to claims
 1. 22. A flat solar collector system with vacuumchambers, characterized in that connection of flat solar collectors withvacuum chambers is performed by attaching the inlet and outletconducting tubes.